Water, waste, and gas — the systems that keep buildings sanitary and safe.
Plumbing engineering is the discipline concerned with the safe delivery of potable water, the sanitary removal of waste, and the distribution of gas and other piped services throughout a building.
Plumbing engineering designs the piping systems that bring clean water in, carry waste and stormwater out, and deliver fuel gas to appliances. In the building context it spans the cold- and hot-water supply (sizing, pressure, and pumping), the drainage, waste, and vent (DWV) system, fixtures and their fixture-unit loads, water heating and recirculation, fuel-gas piping, and protection devices such as backflow preventers and trap seals.
The field is governed closely by plumbing codes because water and waste directly affect public health. An undersized water line starves fixtures, an improperly vented drain can siphon trap seals and admit sewer gas, and a missing backflow preventer can contaminate the potable supply. Much of a plumbing engineer's work is therefore sizing and code compliance — converting fixture units to demand using the Hunter curve, sizing supply and drain piping, laying out venting, and confirming cross-connection control.
Cold- and hot-water piping sized from fixture-unit demand, with pressure, velocity, and booster-pump considerations per the IPC/UPC.
Sanitary drains, soil and waste stacks, traps, and the venting that protects trap seals and prevents siphonage.
Fixture selection and the WSFU/DFU loading model used to convert installed fixtures into design demand.
Storage and tankless water heaters, recirculation, thermal expansion control, and mixing/scald protection.
Fuel-gas pipe sizing per the fuel gas code, plus backflow preventers and cross-connection control protecting the potable supply.
A plumbing engineer designs the water supply, drainage, waste, vent, and fuel-gas piping systems for a building — sizing pipe from fixture-unit demand, laying out drains and vents so traps stay sealed, selecting water heaters and pumps, and producing the riser diagrams and plans that satisfy the plumbing code and the permitting authority.
A plumbing engineer designs the system and performs the sizing calculations and documentation (often stamping drawings as a licensed PE); a plumber installs, repairs, and maintains those systems in the field under a trade license such as journeyman or master plumber. The engineer decides what to build and why; the plumber builds it to code.
Two model codes dominate: the International Plumbing Code (IPC) and the Uniform Plumbing Code (UPC), and the choice depends on which a state or jurisdiction adopts. Fuel-gas piping is covered by the International Fuel Gas Code (IFGC) or NFPA 54, and lead-free requirements come from the federal Safe Drinking Water Act.
Water supply piping is sized by converting installed fixtures into water supply fixture units (WSFU), applying the Hunter demand curve to get probable peak flow in gpm, then selecting pipe that meets the flow within pressure and velocity limits. Drainage is sized from drainage fixture units (DFU) using code tables for stacks, branches, and building drains.